Synthesis and Structural NMR Characterization of Novel PPG/PCL Conetworks Based upon Heterocomplementary Coupling Reactions

A new approach to hybrid model network formation based upon heterocomplementary end‐linking of four‐arm star poly‐ε‐caprolactone (PCL) and linear polypropylene glycol (PPG) precursors is demonstrated. Specifically, hydroxy‐terminated PCL(OH)4 and an amino‐terminated linear PPG(NH2)2 are reacted with a bifunctional coupling agent containing one carboxylic acid chloride group and one oxazinone group. PCL(OH)4 is first reacted with the former in a solution, and the so‐obtained oxazinone‐terminated intermediate is then reacted with PPG(NH2)2 to form a network both in the solution and in the melt. A strong effect of electron‐withdrawing groups on the reactivity of the oxazinone group, and thus on the network formation, is evidenced. Network structure and properties are studied by swelling experiments and low‐field multiple‐quantum (MQ) NMR, which confirm the successful formation of hybrid networks and provide information on the significant network inhomogeneities. On the methodological side, a reliable approach to MQ NMR data analysis for networks of variable degree of inhomogeneity is discussed. Model conetworks obtained from heterocomplementary coupling reactions of polymeric precursors are synthesized and investigated by low‐field multiple‐quantum NMR. The method provides information on network inhomogeneities in terms of a distribution function of an NMR measure of the density of crosslink and entanglement constraints.